Patent GB-1328713-A (GB)
Title: Corpuscular beam scanning microscopes
IPC: H01J37/28
Filed: 1971-07-02
Abstract: 1328713 Electron microscopes; ion beam apparatus MAX-PLANCK-GES ZUR FORDERUNG DER WISSENSCHAFTEN EV 2 July 1971 [31 Aug 1970] 30998/71 Heading H1D A corpuscular beam (electrons or ion) scanning microscope comprises a beam generator to project a beam via deflection system 5, 5<SP>1</SP>, 6, 6<SP>1</SP>, (or alternatively an em. system) to condenser lens 7 which focuses the beam on object 8 for transmission studies, a first diaphragm B, with a plurality of transmissive zones for dark field reproduction, and the combination of a second diaphragm B 2  and detector system, or a detector (Fig. 4, not shown) itself serving as the second diaphragm, the diaphragm or detector respectively having an inner region substantially complementary in its effect to that of the first diaphragm such that those beam components not scattered by the object are not incident upon the detector system, whereas scattered components incident within the inner region are detected, and the second diaphragm and/or detector system having an outer region surrounding the inner region, the surface area of which is larger than the total area of the active zones within the inner region. The output signal may be directed to a TV picture tube. The diaphragm regions are preferably annular and concentric and the outer region has a minimum width at least equal to half the minimum distance of the inner region periphery from the beam axis. The zone widths may be all equal and preferably the first diaphragm is a phase zoned diaphragm allowing only those components to pass to the object, which after traversing the condenser lens, have phases of the same sign, in which case, the closed zone width is preferably larger than the minimum, with correspondingly longer active zones in the second diaphragm and/or detector producing the same signal for reduced load on the object. To compensate for change in the image side apertural zone cone during scanning and penetration of non-scattered components, a second deflector system 10, 10<SP>1</SP> may be included. Non-scattered components may also be countered by making the closed zones of diaphragm B 2  wider than the open zones of B 1 . Preferably the first deflection beam is in two parts so that the redeflected beam intercepts the optical axis in the first diaphragm plane so that the beam always has the same position relative to the first diaphragm and the same condition is obtained for the second diaphragm and/or detector by arranging the zoned plates in co-ordinate planes. B 1  disposed in the condenser focal plane ensures the incident beam angle is constant irrespective of the object point being scanned. B 1  may correct astigmatism by non-circular zones or a stigmator used and may also be between the beam source and deflectors, within lens 7 or between lens 7 and object 8. In Fig. 3 (not shown), B 1  and B 2  are each twice the focal length from the lens 7 and of equal size but other image and object planes are possible. The zoned detectors of (Fig. 4) (not shown) may lead to one or different picture tubes, and electrons scattered at a particular angle may be selected. Detectors (11) to (15) may be reverse biased P-N devices. To improve quality of reproduction or study material composition, electrons of differing energies may be selected in particular non-elastically and elastically scattered electrons, by an electrostatic or magnetic velocity analysis (16) (Fig. 5, not shown).